Convective earrh coil

ABSTRACT

The present invention relates to a method of heat rejection and extraction between a fluid and the earth, providing for a high efficiency convective heat exchanger located in ground water, a means for inducing flow of said ground water at its initial temperature from ground water pool through said heat exchanger, a means of inducing heat transfer from said ground water to said heat transfer fluid or gas, a means of discharging said ground water at a new temperature back into said ground water pool, and a piping system suitable to transport said heat transfer fluid from a thermal load at some remote location at a first temperature, though the said convective heat exchanger and transporting the heat transfer fluid at a new temperature to the location(s) where the thermal energy is utilized.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a method of heat rejection andextraction between a fluid and the earth.

BACKGROUND OF THE INVENTION

Traditionally, if the designer of a heating and/or cooling system forbuilding wanted to substantially improve the energy efficiency of hisbuilding, he could invest in the installation of a ground-source (orearth-coupled) heat-pump system. This would require the installation ofone or more water-source heat-pumps in the building and installing adedicated piping system from the water-source heat-pumps to a groundcoil. The ground coil heating and cooling systems use the earth as anenergy source and heat sink. A series of pipes, commonly called a“loop,” are used to connect the heat pump system to the earth. In a fewinstallations, refrigerant from the heat pump is circulated through theground in a closed loop. However, the more common loops discussed hereuse only water or a water and antifreeze mixture. While the value ofthese systems in the savings of heating and cooling energy has beenprofound, the real world-building owners generally have not been able tojustify the cost, complexity or size of the ground coil in thecompetitive environment they face.

Traditionally, these ground coils have been done in one of two ways.

-   1) Closed Loop Ground Coil Systems

Closed loop systems are becoming the most common. A fluid or refrigerantis circulated through a continuous buried pipe. The length of looppiping varies depending on ground temperature, thermal conductivity ofthe ground, soil moisture, and system design, or

-   2) Open Loop Ground Coil Systems

Used successfully for decades, ground water is drawn from an aquiferthrough one well and is pumped to the surface, passes through somefashion of heat exchanger, and is discharged sometimes to the surfacebut usually to the same aquifer it was drawn from, either through thesame well or a second well at a distance from the first. A special caseof open loop systems is available when a nearby pond or lake can be usedas the water source instead of drilling wells.

Closed Loop Ground Coil Systems general come in three configurations:Horizontal, Vertical, and Pond.

Horizontal closed loop installations are generally most cost-effectivefor small installations, particularly for new construction wheresufficient land area is available. These installations involve buryingpipe in trenches dug with back-hoes or chain trenchers. Up to six pipes,usually in parallel connections, are buried in each trench, with minimumseparations of one fourth of a meter between pipes and 3 to 5 metersbetween trenches. Often slinky shaped coils —overlapping coils ofpipe—are used to increase the heat exchange per meter of trench, butrequire more pipe per ton of capacity. Two-pipe systems may require asmuch as 100 meters of trench per ton of nominal heat exchange capacity.

Vertical closed loops are preferred in many situations. For example,most large commercial buildings and schools use vertical loops becausethe land area required for horizontal loops would be prohibitive.Vertical loops are also used where the soil is too shallow fortrenching. Vertical loops also minimize the disturbance to existinglandscaping. For vertical closed loop systems, one or more U-tubes areinstalled in a well drilled 30 to 150 meters deep. Because conditions inthe ground may vary greatly, loop lengths can range from 40 to 100meters per ton of heat exchange. Multiple drill holes are required formost installations, where the pipes are generally joined in parallel orseries-parallel configurations. Installation costs depend on geologicalconditions and local drilling industry experience.

Both horizontal and vertical closed loop ground coil systems can berelatively expensive compared with above ground air based systems due tothe extensive size requirements. This large area is the result of thelow thermal heat transfer rate of conduction from the pipe to the groundand by poor conduction through the ground.

Pond closed loops are a special kind of closed loop system. Where thereis a pond or stream that is deep enough and with enough flow, closedloop coils can be placed on the pond bottom. Fluid is pumped just as fora conventional closed loop ground system where conditions are suitable,the economics are very attractive, and no aquatic system impacts havebeen shown. Unfortunately, over time, the exposed pipe coils becomefouled with dirt and microbiological growth and lose theireffectiveness.

Open loop systems are the simplest. Generally, two to three gallons perminute per ton of capacity are necessary for effective heat exchange.Since the temperature of ground water is nearly constant throughout theyear, open loops are a popular option in areas where they are permitted.Open loop systems do have some associated challenges: (1) Local groundwater chemical conditions can lead to fouling the heat pump's heatexchanger particularly if oxygen, carbon dioxide and/or other gases areintroduced or disturbed in solution in the water. (2) Increasingenvironmental concerns mean that local officials often requirepermitting to assure compliance with regulations concerning water useand acceptable water discharge methods. (3) As the water is returned tothe aquifer, challenges arise with re-injection flow rates, oxygenatingthe water, creating a vacuum at the high point of the loop, etc. (4) Aopen well system may not be practical where the water table is verydeep, because pumping requirements would become prohibitive.

Open Loop Ground Coil Systems general come in three configurations:Standing well, Multiple well and Pond.

Open Loops—Standing Wells

Standing wells, also called turbulent wells, may be as deep as 500meters, withdraw water from the bottom of the well, circulate it throughthe heat pump's heat exchanger, and return it to the top of the watercolumn in the same well. Some systems operate with less than 30 metersof well per ton of nominal capacity. Short circuiting of return water tosupply and oxygenating the water are some of the concerns with thisapproach.

Multiple wells

By providing distance between supply and discharge wells, the shortcircuiting of return water to supply is usually avoided. Howeveradditional wells and piping will be required and the ability of thedischarge well to accept the re-injection flow may be limited. Inaddition, there may be permitting issues.

Pond or lake water can be drawn out, pumped through a heat exchanger andreturned to the pond. Debris, scaling and fouling of the piping systemand heat exchanger are concerns with this approach.

While ground source systems provide energy savings, low maintenance, andminimum noise, the relatively high cost of constructing the ground coilreduces their popularity.

To avoid the high costs and problems associated with open and closedloop ground coils; this novel invention demonstrates a new means ofthermally coupling heating and cooling systems with the earth.

Prior art in ground coil systems focused on either using vast array ofpipes in the ground or pond as the heat exchanger (closed loop system)or ground water was brought above grade to an efficient heat exchangerusing forced convection (open loop system).

This innovative invention combines the advantages of open systems (highheat transfer rates associated with convective heat transfer) with theadvantages of closed loop systems (no removal of water from itslocation, with associated problems of permitting, re-injecting andaerating). This novel approach, locates a high efficiency, convectionbased, heat transfer coil in the aquifer or pond. Ground or pond wateris forced to flow through one side of the heat exchanger either throughthe known principle of natural convection, or with the assistance of amechanical means, providing forced convection. On the other side of theheat exchanger, a fluid or refrigerant transfers the thermal energy towhere it is needed by a closed loop piping system. Since ground water isnever removed from its natural location, concerns of contamination,aeration, permitting, and re-injection are avoided.

An additional unforeseen advantage of this unique invention is that itpromotes the natural thermal stratification of the ground water. Thismeans that cooler water settles below warmer water. This allows thesystem designer to treat the ground water as a huge thermal storagedevice. During times when heat is rejected to the ground water, coolwater is drawn from lower levels (either by natural convection or amechanical means), and heated and stored in upper levels. The poorthermal characteristics of the earth combined with the stratificationeffect prevent the thermal energy from warming the cooler water below.Then when heat is need by the building, the convection flow direction isreversed (either by natural convection or a mechanical means), and warmwater is cooled and stored in the lower level of the ground water.Again, the poor thermal characteristics of the earth combined with thestratification effect prevent the thermal energy from cooling the warmerwater above. This thermal storage feature could allow thermal energystored during the day to be used for heat at night. It is possible thateven heat energy stored over the summer could be used in the winter.Also with proper design of the distribution system within the building,the heating and cooling energy could be transferred to their needed usesby direct heat transfer, without the need of a heat pump. For example,the energy removed to cool a house in August, could be used to melt snowfrom a driveway in January, with only the power consumption of a smallpump.

Additional benefits of this novel invention accrue from thesubstantially improved heat transfer rate of the heat exchanger comparedto conventional closed loop. This allows for a closure approach betweenthe temperature of the heat transfer fluid and the ground fluid. This ofcourse improves the efficiency of the whole system and saves energy.This offers an addition advantage in cool climates (ground temperaturesbelow 10 to 15 degrees C.) when the system is used to extract heat fromthe ground. Conventional ground coils may have as much as a 15 degreetotal temperature difference between the working fluid and the ground,meaning the fluid temperature drops below freezing and requiresantifreeze. This new invention can provide an approach temperature of 5degrees or less, avoiding the need for antifreeze and its associatedcost, energy and pumping penalties, and ground water contaminationconcerns.

An additional unforeseen benefit of this novel invention is that thedepth of the aquifer is no longer a deterrent to using an earth coil.Going down hundreds of meters to find an aquifer will not adverselyaffect pumping energy, since with a closed loop the return water goingdown pushes the supply water back up.

The present invention solves the problems, reduces the initial cost andimproves the performance of conventional earth coil systems. The properdesign and engineering, a single well could provide heating and coolingfor a large building. Moreover, because the systems is simple and canrequire only one well, it is readily fit for existing buildings. Inaddition, this single well can serve multiple functions, such as housinga conventional well pump providing water for domestic irrigation or firefighting. It can be appreciated that the cost of installing such anearth coil system is relatively low, making it more enticing to theexisting building owner and building developers.

SUMMARY OF THE INVENTION

Thus and in accordance with a first aspect of the present invention,there is provided a system for heat rejection and extraction between aheat transfer fluid or gas and the earth, providing for a highefficiency convective heat exchanger located in ground water, a meansfor inducing flow of said ground water at its initial temperature fromground water pool through said heat exchanger, a means of inducing heattransfer from said ground water to said heat transfer fluid or gas, ameans of discharging said ground water at a new temperature back intosaid ground water pool, and a piping system suitable to transport saidheat transfer fluid from a thermal load at some remote location at afirst temperature, though the said convective heat exchanger andtransporting the heat transfer fluid at a new temperature to thelocation(s) where the thermal energy is utilized.

Preferably said ground water can be below ground surface water in a wellor cave, or above ground surface water in a pond, lake, stream or ocean.

Preferably said heat transfer fluid is a substance that would not harmor deteriorate the quality of the said ground water if it were to leakinto the ground water, including potable water, water with non-toxicadditives, or other environmentally friendly fluid or gases.

Preferably said convective heat exchanger utilizes the efficiencies ofconvective heat transfer to thermally link the said ground water to thesaid heat transfer fluid.

Preferably said convective heat exchanger utilizes efficient heatexchanger design, including tube-in-tube, spiral tubing, finned orenhanced tubing, or a rectangular or circular plate design.

Preferably said convective heat exchanger utilizes thermally conductivematerials that are suitable for contact with the said ground water andsaid heat transfer fluid, such as copper, cupronickel, stainless steel,or plastic.

Preferably said means for inducing flow of said ground water at itsinitial temperature from said ground water pool through said heatexchanger is an enclosed vertical chamber of sufficient length togenerate natural fluid flow forces due to the difference in temperatureand density of said ground water entering the said heat exchanger at itsinitial temperature with the said ground water leaving the said heatexchanger at its said new temperature.

Advantageously said means for inducing flow of said ground water throughsaid heat exchanger could be a mechanical pump. Preferably saidmechanical pump could be electrically driven or could be driven by theflow of the heat transfer fluid acting upon an impeller, which drivessaid pump. The said impeller could be mechanically coupled via a sealedshaft, or preferably, could be magnetically coupled.

Preferably said means for inducing flow of said ground water at itsinitial temperature from said ground water pool includes a means offiltering out particles that would foul said convective heat transfermeans, and a means of eliminating or back flushing said particles.

Preferably said heat transfer fluid piping system utilizes materialsthat are suitable for contact with the said ground water and said heattransfer fluid, such as copper, cupronickel, stainless steel, orplastic.

Advantageously, the said means for inducing flow of said ground watermay also promote the natural stratification of the ground water intothermal layers, allowing for storage of thermal energy. Preferably saidsystem for heat rejection and extraction between a heat transfer fluidor gas and the earth water cooling means is connected to other heatsinks or heat sources, such as a hydronic snowmelt system (a series oftubes buried in or beneath sidewalks and driveways near the saidbuilding) or solar energy panels, or waste heat collection system andcontrols are provided to allow for the optimum storage and removal ofthermal energy on a daily and seasonal basis.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing aspects and many of the attendant advantage of thisinvention will become more readily appreciated as the same becomesbetter understood by reference to the following detailed description,when taken in conjunction with the accompanying drawing, wherein:

FIG. 1 is a section view of the present invention for an undergroundaquifer incorporating the present invention using ground water directlyas accessed through a deep well.

FIG. 2 is a section view of the present invention for a lakeincorporating the present invention using ground water and incorporatinga heat transfer driven pump to induce ground water flow.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, a portion of an aquifer some depths below the earthsurface 1 is generally shown by reference numeral 2. A well 3 is drilledfrom the earth surface 1 until it reaches the desired aquifer 2. Pipes 4and 5 for supplying and returning the heat transfer fluid from thethermal load 6 to the convective earth coil 7 are run below the earth'ssurface 1 (preferably below the frost line 8) to the well 3, and downthe well 3 to the convective earth coil 7. In FIG. 1, the convectiveearth coil 7 is generally comprised of inlet 9, a vertical chamber 10, aconvective heat exchanger 11, and a discharge outlet 12. In FIG. 1 theconvective heat exchanger 11 is represented as a spiral tube within atube.

The convective earth coil can be used to inject heat into the ground orextract heat energy from the ground. In the illustrated embodiment, inoperation in the heat injection mode, warm heat transfer fluid flowsfrom the thermal load 6 through pipe 4 into the top portion of theconvective heat exchanger 11. Thermal energy is transferred from theheat transfer fluid through the convective heat exchanger 11 to theground water 2. The thermal energy increases the temperature of theground water 2 that is in contact with the convective heat exchanger 11.The increase in temperature causes the warmer water to expand in volume,proportionately decreasing its density. The warmer, lower density water13 will rise to the top of the aquifer 2 and cooler, denser ground water14 will be drawn in from below the ground coil to replace it. Thisupward flow action within the convective earth coil 7 will produce aflow of warm water 13 filling and stratifying in the upper layers of theaquifer 2. The layers of warm water will gradually work their way downto replace the cool water 14 being drawn in at the base of theconvective earth coil 7.

In the illustrated embodiment, in operation in the heat extraction mode,cool heat transfer fluid flows from the thermal load 6 through pipe 5into the bottom portion of the convective heat exchanger 11. Thermalenergy is transferred from ground water 2 through the convective heatexchanger 11 to the cool heat transfer fluid. The thermal energy lossdecreases the temperature of the ground water 2 that is in contact withthe convective heat exchanger 11. The decrease in temperature causes thecooler water to contact in volume, proportionately increasing itsdensity. The cooler, higher density water 14 will drop to the bottom ofthe aquifer 2 and warmer ground water 13 will be drawn in from above theground coil to replace it. This downward flow action within theconvective earth coil 7 will produce a flow of cool water 14 filling andstratifying in the lower layers of the aquifer 2. The layers of coolwater will gradually work their way up to replace the warm water 14being drawn in at the top of the convective earth coil 7.

Referring to FIG. 2, a lake is generally shown by reference numeral 2.Pipes 4 and 5 for supplying and returning the heat transfer fluid fromthe thermal load (not shown) to the convective earth coil 7 are runbelow the earth's surface 1 (preferably below the frost line 8) to thelake 2, and to the convective earth coil 7. In FIG. 2, the convectiveearth coil 7 is generally comprised of inlet 9, a vertical chamber 10, aconvective heat exchanger 11, a discharge outlet 12, and a means ofanchoring and support the assembly 3.

In FIG. 2 the convective heat exchanger 10 is represented as a platetype heat exchanger. The illustrated embodiment includes screens at theinlet 9 and discharge 12 to keep debris and fish out of the heatexchanger. The illustrated embodiment includes an impeller 15 in theheat transfer stream that is magnetically coupled to a pump 16 in thelake water stream 14.

The convective earth coil can be used to inject heat into the lake orextract heat energy from the lake. In the illustrated embodiment, inoperation in the heat injection mode, warm heat transfer fluid flowsfrom the thermal load through pipe 4 into the top portion of theconvective heat exchanger 12. Thermal energy is transferred from theheat transfer fluid through the convective heat exchanger 12 to the lakewater 2. The thermal energy increases the temperature of the lake water2 that is in contact with the convective heat exchanger 12. The increasein temperature causes the warmer water to expand in volume,proportionately decreasing its density. The warmer, lower density water13 will rise to the top of the lake 2 and cooler, denser lake water 14will be drawn in from below the convective earth coil 7 through thefilter screen 9 to replace it. This upward flow action within theconvective earth coil 7 will produce a flow of warm water 13 filling andstratifying in the upper layers of the lake 2. The layers of warm waterwill gradually work their way down to replace the cool water 14 beingdrawn in at the base of the convective earth coil 7. The heat transferfluid leaving the heat exchanger acts on impeller 15, which ismagnetically coupled to pump 16. Pump 16 assists the natural convectiveflow, and increase the flow of lake water 2.

In the illustrated embodiment, in operation in the heat extraction mode,cool heat transfer fluid flows from the thermal load through pipe 5 intothe bottom portion of the convective heat exchanger 12. Thermal energyis transferred from the heat transfer fluid through the convective heatexchanger 12 to the lake water 2. The thermal energy decreases thetemperature of the lake water 2 that is in contact with the convectiveheat exchanger 12. The decrease in temperature causes the cooler waterto contact in volume, proportionately increasing its density. Thecooler, higher density water 13 will sink to the bottom of the lake 2and cooler, denser lake water 14 will be drawn in from above theconvective earth coil 7 through the filter screen 12 to replace it. Thisdownward flow action within the convective earth coil 7 will produce aflow of cool water 13 filling and stratifying in the lower layers of thelake 2. The layers of cool water will gradually work their way up toreplace the warm water 14 being drawn in at the top of the convectiveearth coil 7. The heat transfer fluid entering the heat exchanger actson impeller 15, which is magnetically coupled to pump 16. Pump 16assists the natural convective flow, and increase the flow of lake water2.

Although described above are types of convective earth coils, it can beappreciated by those skilled in the art that other methods of heatexchange may be utilised.

Additional options include: 1) Transferring the heat energy via a heatexchanger to a series of tubes buried in or beneath sidewalks anddriveways, thereby providing both building heat rejection and a snowmelt system, 2) Storing thermal energy from a solar collector during theday and transfer the energy to domestic hot water the following morning.

As can be seen in the description above, earth heat extraction,injection and storage may be accomplished by utilizing convective heatexchange devices within the ground water. Moreover, in contrast to theprior art, the convective heat coil 7 is relatively simple inmanufacture as compared with closed loop earth coils. As can beappreciated by those skilled in the art, the improved heat transfercharacteristics of the convective earth coil may provide cool enoughcold water temperatures, or warm enough hot water temperatures thateliminate the need for a complex heat exchanger including an evaporatorand compressor in order to generate cooling or heating from a moremoderate temperature fluid.

Additionally, the compressor type heat exchangers require large amountsof power and are relatively noisy. In contrast, the circulating pumpsrequire only a small amount of power.

It is, of course, to be understood that the invention is not intended tobe restricted to the details of the above embodiments which aredescribed by way of example only.

1. A system for heat rejection and extraction between a heat transferfluid or gas and the earth, providing for a high efficiency convectiveheat exchanger located in ground water, a means for inducing flow ofsaid ground water at its initial temperature from said ground waterthrough said heat exchanger, a means of inducing heat transfer from saidground water to said heat transfer fluid or gas, a means of dischargingsaid ground water at a new temperature back into said ground water, anda piping system suitable to transport said heat transfer fluid from athermal load at some remote location at a first temperature, though thesaid convective heat exchanger and transporting the heat transfer fluidat a new temperature to the location(s) where the thermal energy isutilized.
 2. The heat rejection and extraction system in claim 1 whereinsaid ground water can be below ground surface water in a well or cave,or above ground surface water in a pond, lake, stream or ocean.
 3. Theheat rejection and extraction system in claim 1 wherein said heattransfer fluid is a substance that would not harm or deteriorate thequality of the said ground water if it were to leak into the groundwater, including water, water with non-toxic additives, or otherenvironmentally friendly fluid or gases.
 4. The heat rejection andextraction system in claim 1 wherein said convective heat exchangerutilizes the efficiencies of convective heat transfer to thermally linkthe said ground water to the said heat transfer fluid.
 5. The heatrejection and extraction system in claim 1 wherein said convective heatexchanger utilizes efficient heat exchanger design, includingtube-in-tube, spiral tubing, finned tubing, or a rectangular or circularplate design.
 6. The heat rejection and extraction system in claim 1wherein said convective heat exchanger utilizes thermally conductivematerials that are suitable for contact with the said ground water andsaid heat transfer fluid, such as copper, cupronickel, stainless steel,or plastic.
 7. The heat rejection and extraction system in claim 1wherein said means for inducing flow of said ground water at its initialtemperature from said ground water pool through said heat exchanger isan enclosed vertical chamber of sufficient length to generate naturalfluid flow forces due to the difference in temperature and density ofsaid ground water entering the said heat exchanger at its initialtemperature with the said ground water leaving the said heat exchangerat its said new temperature.
 8. The heat rejection and extraction systemin claim 1 wherein said means for inducing flow of said ground waterthrough said heat exchanger could be a mechanical pump.
 9. Themechanical pump in claim 8 could be electrically driven or could bedriven by the flow of the heat transfer fluid acting upon an impeller,which drives said pump, the said impeller could be mechanically coupledvia a sealed shaft, or could be magnetically coupled.
 10. The mechanicalpump in claim 8 use centrifugal, displacement or other known pumpingstrategies.
 11. The heat rejection and extraction system in claim 1wherein said heat transfer fluid piping system utilizes materials thatare suitable for contact with the said ground water and said heattransfer fluid, such as copper, cupronickel, stainless steel, orplastic.
 12. The heat rejection and extraction system in claim 1 whereinthe said means for inducing flow of said ground water may also promotethe natural stratification of the ground water into thermal layers,allowing for storage of thermal energy.
 13. The heat rejection andextraction system in claim 1 wherein said system for heat rejection andextraction between a heat transfer fluid or gas and the earth watercooling means is connected to other heat sinks or heat sources, such asspace heating or cooling system, a potable water heating system, ahydronic snowmelt system (a series of tubes buried in or beneathsidewalks and driveways near the said building) or solar energy panels,or waste heat collection system and controls are provided to allow forthe optimum storage and removal of thermal energy on a daily andseasonal basis.